Some effects of Expansion due to Heating
- A small gap is provided between the rails on railway tracks to make provision for the expansion of rails during summer, otherwise, the rails may bulge due to expansion causing train accidents.
- If a metal wire is used in a pendulum, its length changes with temperature. During summer, its length increases and thus, increasing its period and the pendulum clocks go slow in summer. During winter, the length decreases and hence, its period decreases. Thus, the pendulum clocks go fast during summer.
- In a cartwheel, the iron tyres are manufactured so that their diameter is slightly less than the wooden wheel on which they are fitted. The iron tyres are heated first. They expand and can be fitted easily into the wooden wheels. When cooled the iron wheels firmly grip the wooden wheels.
- Soda or soft drink bottles are made of thick glass. The reason for this is as follows-when a gas is heated in a closed container, its pressure increases. In a soda bottle this is exactly what happens, during summer heat, the soda bottles may explode due to pressure increase inside the bottle. Hence soda bottles are made of thick glass to withstand pressure increase.
Anomalous expansion of Water:
Generally, all liquids expand due to heating. But water behaves in a peculiar way when heated from 0oC to 4oC. On heating from 0oC up to 4oC its volume decreases, reaches a minimum at 4oC such that the density of water is maximum at 4oC on heating further, water behaves like any other liquid. Similarly, during cooling process, the volume of water decreases up to 4oC, reaches a minimum at 4oC, if further cooled up to 0o C, its volume increases instead of decreasing and hence, density of water at 0oC is lesser than that at 4oC. Water freezes to ice at 0oC. Being less dense than water, ice floats on water. Beyond 4oC, water behaves like any other liquid.
This unique feature of water between 0 and 40C, is a boon to aquatic animals. Let us see how-In cold countries and Polar Regions during winter, the temperature goes below 00C. In lakes and ponds when water at the surface reaches 40C, it is densest and goes to the bottom. When the temperature further reduces, only surface layers of water freeze whereas at the bottom water remains at 40C. Aquatic animals live comfortably in water at 40C ,whereas, outside temperatures may go much less than that.
